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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3326
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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I have a Kenworth T 300 that I am having an issue with some

Customer Question

Customer: Hi There, I have a Kenworth T 300 that I am having an issue with some sort of buzzer going off, and it goes away if I turn on the lights and fan motor. The Alt guage also goes from 13.8 to 12 and back and forth if it sits over night in the cold. Once it warms up and I am driving its all good. I have replaced the headlight switch, checked grounds and about anything else I could come up with. Seems to me some type of relay is bad or going bad but i'm not sure any help would be great. It has a cummings 315HP
JA: Thanks. Can you give me any more details about your issue?
Customer: Like what Info ? I gave you everything I know at this point. The buzzer is like some type of Alarm I'm thinking over charge or something
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Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 1 year ago.

My name is ***** ***** I will assist you.

Have you checked the alternator and did a full test on it? I know it sounds silly, but when that alternator messes up and the diode goes bad, it causes all kinds of back-feed where you get the buzzing noises in the cab. I would check there first before trying to look for other "ghosts" in the wiring behind the dash, relays, etc. The alternator is the most common point for weird buzzing when the lights are on or the fan. A lot of times you can also hear it on the back of the radio when the radio is off.

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Customer: replied 1 year ago.
Hi there , yes we had the all checked at the dealer and we did our self and everything appears to be fine
Expert:  Jeremy replied 1 year ago.


The buzzer sounds like a safety alarm or just a weird buzzing, annoying sound that is light and hard to locate?

Expert:  Jeremy replied 1 year ago.

Have you noticed any flickering in the dash lights at all?

Customer: replied 1 year ago.
Well no light flickering on dash or anywhere , there's something up and it's driving us nuts that we can't find it , we just don't know enough about this big truck electrical systems , there is some safety buzzer that's going off for sure can u tell me what's things on this truck would be tues into the buzzer system and any Type of relays that might be having an issue causing my symptoms ?
Expert:  Jeremy replied 1 year ago.

If you have a safety buzzer going off, that can be a air leak on the truck or a code in the engine. Do you have a check engine light or does the air gauge read full? There could be an issue with the sensor/switch for the air brake causing the buzzer to go off. Maybe even a short in the buzzer itself on the back of the dash panel where the speedometer is.

Unfortunately Kenworth offers very little access to these trucks for wiring diagrams. I can pull up the next series of the truck like the T400 and T600 series, but the T300 is locked. They still haven't allowed access to that one under the right to repair just yet. So I am unable to obtain a diagram at this time.

Expert:  Jeremy replied 1 year ago.

I see you viewed this and this is still showing as a open question due to no positive (3 stars or more) rating.

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